Antenna “ranges” or anechoic chambers are used for testing a wide variety of devices. Many types of units under test (UUT), such as multi-mode seekers, for example, operate, and therefore must be tested, at multiple wavelengths. Conventional systems for testing such devices include a number of spatially distributed discrete signal sources that provide multiple wavelength signals and are subject to mis-alignment in position and angle. Typically these sources cannot be easily co-located or angularly co-aligned. Alternatively, discrete tests can be performed at different test stations configured to operate at different wavelengths. However, such test facilities require either or both of significant metrology to calibrate the alignment between UUT and test source in each measurement chamber, or significant floor space so as to move the sources far a-field from the multimode seeker UUT. Another known structure is disclosed in U.S. Pat. No. 5,012,250, which discloses an infrared (IR) radiator disposed in a center of an RF (radio frequency) horn radiator to provide an IR and an RF source. However, such structure suffers from compromised performance due to numerous infirmities including blockage imposed by the IR source in the RF radiator.